9 replies to this topic

[WaterDragon]

Hi I was wondering the weight difference that 100 tanks make over 80.

I was thinking that one would use more weight with 100 the with 80 because of the volume of air that is in the tank to start with and the weight and that it woud be more boyent and 15 feet the an 8- tank would be.

But Wreck Wrench brough up a go point about there are different 100 come in steel and alumin I have only dove with alumin tankds so I didn't ferure on stell tanks.

So if one use 100 alumin tanks instead of 80 would one use more or less weight?

And how whot that copare to stell tanks?

Thanks Jerry

[ScubaDadMiami]

There are high pressure tanks, low pressure tanks, and even some differences between the pressures of different manufacturers for the same pressure and volume tanks. In general, steels are more negative than aluminums, allowing the diver to carry less weight. However, beyond this generalization, it is best to check on the information of the manufacturer and/or your local dive store.

[dive1dennis]

Jerry, from your post I was not sure if you are talking about a steel or aluminum 100. But ether way it is simple to calculate the difference on your weight belt. And that beats guessing

Just look up the empty buoyancy of the two tanks you are looking at, and compare the buoyancy numbers between the two. The change in buoyancy will be tell you what adjustment to make on your weight belt. These specs. are available on line from the manufacturers.

When I go from an AL80 (Catalina) to a high pressure (3442PSI Worthington) steel 120 I drop about 5lb. or 6lb.
In my example, from Catalina's site, my AL80 is +4lb. buoyant when empty.
From Worthington's site, my X7-120 is -2 lb. buoyant when empty.
The difference is 6 lb, so I take 6 lb. off my weight belt (the 120 is more negative).

If you are talking about an aluminum 100, from Luxfer's site an empty 80 is +4.4lb buoyant, an empty 100 is +3.06lb. buoyant. So 4.4lb - 3.06 = 1.34lb. You would take about 1 lb. off your weight belt (the AL100 is more negative). I looked up Luxfer because I did not see a regular 100 cu. ft. tank on Catalina's page.

Hope this helps!

[WaterDragon]

Jerry, from your post I was not sure if you are talking about a steel or aluminum 100. But ether way it is simple to calculate the difference on your weight belt. And that beats guessing

Just look up the empty buoyancy of the two tanks you are looking at, and compare the buoyancy numbers between the two. The change in buoyancy will be tell you what adjustment to make on your weight belt. These specs. are available on line from the manufacturers.

When I go from an AL80 (Catalina) to a high pressure (3442PSI Worthington) steel 120 I drop about 5lb. or 6lb.
In my example, from Catalina's site, my AL80 is +4lb. buoyant when empty.
From Worthington's site, my X7-120 is -2 lb. buoyant when empty.
The difference is 6 lb, so I take 6 lb. off my weight belt (the 120 is more negative).

If you are talking about an aluminum 100, from Luxfer's site an empty 80 is +4.4lb buoyant, an empty 100 is +3.06lb. buoyant. So 4.4lb - 3.06 = 1.34lb. You would take about 1 lb. off your weight belt (the AL100 is more negative). I looked up Luxfer because I did not see a regular 100 cu. ft. tank on Catalina's page.

Hope this helps!

Thnaks That explans quick a bit. Did not know that you could look up the boyence of a tank.

I was tought better to be a little over weight then under so leaving the 1lb weight on would be ok.
I would be better off just use the same amount of weight I used with the alumin.?

That is if I use a alumin 100 tank not a steel tank.

[Penguin]

So if one use 100 alumin tanks instead of 80 would one use more or less weight?

And how whould that compare to steel tanks?

________________________________________________________________________________
______
Jerry
All of the tank manufacturers post buoyancy characteristics of each of their tanks. Your dive shop should be able to pull that info and give you the exact buoyancy characteristics of their tanks both full and at your 15' safety stop.

[jextract]

You can look up the particular data for your tank here:
http://members.aol.c.../tankspecs.html

or here:

http://www.nitroxdiv.../Tank-Specs.htm

[Dive_Girl]

I recalled what a great reference the links Jexy provided above were. Thanks Jexy!

[Racer184]

I have Catalina 100s. On the very very very rare occasion I use a aluminum 80, I add 4 pounds.

[peterbj7]

You only need to look up the buoyancy if a tank's volume is measured in the American way. If it's according to the norm in the rest of the world all you need to know is the volume and the weight of the empty tank and you can calculate it from there.

I'm not talking about cu.ft. compared with litres, but whether the stated volume is that of the tank itself (the "water volume") or that of the air at surface conditions that could be compressed into it at its "rated pressure". The latter is used in the USA and countries influenced by it, the former is the norm in Europe and most other countries of the world (and is IMHO far more logical and useful!). If you're not sure of how they relate to each other, the "normal" US tank of a 80 cu.ft. holds around 10% less air than the normal European tank of 12 litres.

Some people don't like the way a near-empty aluminum tank becomes positive and lifts the BCD off their shoulders. This can be overcome by having a small camband with a 4lb weight and fixing it to the tank, obviously reducing the other weight you carry by that amount!

[Bubble2Bubble]

WaterDragon
Great Thread

Learning how to read the stamped numbers on the tank you have already or the tank your thinking of buying is important. I have several al80s and some al60s, at least two of my al80s actualy have weight manufactured in them to allow for the low/empty tank buoyancy, and some other 80s are rated for 3300 psi.. not to mention hydro dates, alloy, date of manufacture etc.. buoyancy is a never ending battle because as soon as you change one piece of your gear like a primary light you add weight or when you have a camera in a housing you add buoyancy. Its a good Idea to write down in your log book on each dive what you had as far as equipment, safety devices, weights so you will know down the road what your buoyancy/weight will be using XYZ gear.


Mike

Edited by Bubble2Bubble, 31 July 2008 - 07:19 PM.